1. Field of the Invention
This invention relates to a bleaching composition which is employed for processing silver halide color photographic light-sensitive materials and more particularly, to a bleaching composition containing as a bleaching agent a particular combination including an organic acid-iron (III) complex salt, a bromate salt, and a water-soluble halogenide.
2. Description of the Prior Art
In typical processes for photographic processing of a silver halide color photographic light-sensitive material, the light-sensitive material (i.e., the silver halide photographic emulsion, which may be fogged in advance of the photographic exposure) is exposed to an imagewise pattern of light, and then development-processed with a developing solution containing an aromatic primary amine developing agent in the presence of dye-forming couplers, to produce a color image and developed silver simultaneously. The developed silver thus produced is converted into a halide thereof again in the subsequent bleaching step, and then removed from the material by receiving a fixing or a bleaching-fixing treatment.
Hitherto, ferricyanates, dichromates, ferrates (III), organic acid-iron (III) complex salts, persulfates and so on have been known to be usable as bleaching agents in bleaching compositions to be employed in the bleaching step, while water-soluble halogenides such as sodium chloride, ammonium chloride, sodium bromide and the like have been known to be usable as rehalogenating agents therein. Of the above-described bleaching agents, ferricyanates are preferred from the viewpoint that they have bleaching rates (oxidizing rates) high enough to completely oxidize developed silver within a practically permissible period of time. However, a bleaching solution in which a ferricyanate is employed as a bleaching agent liberates cyan ion on photolysis, to cause an environmental pollution problem, and therefore some step(s) for transforming the used solution to a completely harmless form must be taken.
In the case of another bleaching solution in which a dichromate is used as the bleaching agent it is also necessary to take some step(s) for transforming the waste solution to a completely harmless form so that the waste solution does not discharge dichromic acid ion, which is harmful from the viewpoint of environmental concerns.
Compositions as described above, which require such additional treatments so as to render the wastes thereof completely harmless, suffer from the defect that practice of such measures in an industrial scale is complex and costly.
With the intention of overcoming the defects of ferricyanate and dichromate bleaching compositions, it has been attempted to employ inorganic ferrates (III), organic acid-iron (III) complex salts, persulfates, etc., as the bleaching agent.
Bleaching solutions containing inorganic ferrates (III) or persulfates not only cause environmental pollution problems, but also suffer from the disadvantage that they corrode materials of which the processing machine and tanks for processing solutions are typically constructed. In addition, persulfates are dangerous materials which are inconvenient to handle, since great care must be taken in storing and transporting them. Among bleaching agents that do not possess such disadvantages as described above are organic acid-iron (III) complex salts.
However, bleaching solutions in which organic acid-iron (III) complex salts are employed as the bleaching agent suffer from the disadvantages that they not only have insufficient bleaching power (because their oxidizing power is low), but also tend to cause poor color-development when used in the case of relatively short time processing of a color photosensitive material. This poor color-development is presumed to be caused by the incomplete oxidation of the reaction products of couplers produced by color development with the color developer in the bleaching step. Namely, the incomplete oxidation is believed to bring about such a situation wherein the reaction products remain mainly in a form of a colorless leuco dye, and, consequently, they are only partially converted to their respective ultimate dyes.
Though it is possible to convert these leuco dyes into their respective photographic dyes through oxidation even when the bleaching solution containing an organic acid-iron (III) complex salt is used, the bleaching processing using such a bleaching solution must be continued for a long time in order to achieve the complete conversion of the leuco dyes into the final color photographic dyes. However, it is very difficult to elongate the processing time for bleaching, since the photographic processing must necessarily be limited in time, for instance, in the case wherein the photographic processing is carried out using an automatic developing machine or the like.
On the other hand, addition of bromate ion in the form of alkali metal salt or ammonium salt to the bleaching solution containing an organic acid-iron (III) complex salt can prevent the occurrence of poor color-development by facilitating oxidation of leuco dyes within a period of time required usually for bleach to result in the conversion to photographic dyes. However, the use of such a bleaching solution causes new problems. One problem is the occurrence of stain due to a strengthening of the oxidizing power of the bleaching solution. Particularly, magenta stain and yellow stain are apt to be caused in light-sensitive materials by such a bleaching step. The other problem lies in the fact that the power of the bleaching solution decreases with the lapse of time because bromates are unstable in the bleaching solution, and therefore tend to decompose. This indicates that the bleaching solution to which a bromate is added has a short life. Consequently, not only does the regeneration of the bleaching solution for purposes of reuse thereof become difficult, but also it is necessary that fresh bleaching solution be added in a large amount as the processing proceeds. Accordingly, in the case where such a bleaching solution as described above is used, large amounts of reagents are required for the bleaching processing, thus resulting in the increased cost of processing, in other words, uneconomical processing.